1. Field of the Invention
The present invention relates generally to optical switching, and particularly to protection switching in a two-fiber optical channel shared protection ring.
2. Technical Background
In many areas of the telecommunications network, fiber optic systems have displaced electrical transport systems because light propagating in optical fibers can carry more information, over longer distances. Optical fiber is also an ideal transmission medium because it is characterized by low transmission losses, low interference, and potentially high bandwidth. However, in many fiber optic systems, most of the switching is still being performed in the electrical domain. In order to take full advantage of the high bandwidth of fiber optic systems, switching functionality has begun to migrate from the electrical layer to the optical layer. At the same time, optical network architectures are becoming increasingly complex. Early architectures were mere point-to-point links. Presently, network designers are considering both optical protection rings, and interconnected optical protection rings.
Optical protection ring topologies are currently being deployed by network providers because of their cost savings, survivability, and ability to self-heal. Ring topologies typically include a plurality of client access nodes that are interconnected by at least two optical fibers to form a ring. Traffic is transmitted from node to node around the ring. Optical protection rings can survive and self-heal from ring fault conditions by providing duplicate and geographically diverse paths for all of the client traffic propagating on the ring. In a two-fiber ring, this is accomplished by providing two fibers that carry working traffic in opposite directions. Each fiber reserves approximately half of its bandwidth for protection purposes. Thus, if a cable is cut between two nodes, or if a wavelength channel transmitter becomes disabled at a particular node, or if there is a switch fabric failure, the ring will detect the fault condition, and route traffic around the damaged network component using the protection bandwidth until a repair can be effected.
Optical shared protection rings are designed to perform protection switching in the optical layer. Protection switching in the optical layer is desirable because it enables the protection mechanism to operate independently of the bit-rate and format of the optical channel. Each channel in a conventional two-fiber bi-directional optical channel shared protection ring has two associated wavelengths. One wavelength propagates in a clock-wise direction in one fiber. The other wavelength propagates in a counter-clock-wise direction in the other fiber. Each wavelength is typically switched using two separate uni-directional switches disposed in each node. What is needed is an optical protection switch that accommodates each wavelength signal in a bi-directional channel to thereby replace the two uni-directional switches used in the conventional system.
The present invention is directed to a bi-directional optical protection switch that replaces the two uni-directional switches used in the conventional system described above. For every channel in a protection ring, if a node adds traffic from one wavelength, it must drop traffic on the other wavelength return path. This symmetry causes the states of the two uni-directional switches in the conventional design to be mirrors of each other. The present invention takes advantage of this fixed relationship and by replacing the conventional uni-directional pair of switches with one bi-directional switch.
One aspect of the present invention is directed to a protection switch for use in a node of a two-fiber optical shared protection ring. The two-fiber optical shared protection ring propagates at least one bi-directional channel. Each bi-directional channel includes a working first wavelength signal and a working second wavelength signal. One fiber in the two-fiber optical channel shared protection ring propagates the working first wavelength signal in a first direction and the other fiber in the two-fiber optical channel shared protection ring propagating the working second wavelength signal in a second direction opposite the first direction. The switch includes an Nxc3x97N optical switch fabric system disposed in the node. The Nxc3x97N optical switch fabric includes 2N input/output (I/O) ports, wherein N is four, or an integer multiple of four. Each optical switch fabric is configured to switch at least one bi-directional channel. At least N three-port optical devices are coupled to N of the I/O ports. Each three-port optical device includes a bi-directional port coupled to an I/O port. The bi-directional port is configured to propagate the at least one bi-directional channel. In another aspect, the present invention includes a two-fiber optical channel shared protection ring. The two-fiber optical shared protection ring propagates at least one bi-directional channel. Each bi-directional channel includes a working first wavelength signal and a working second wavelength signal. One fiber in the two-fiber optical channel shared protection ring propagates the working first wavelength signal in a first direction and the other fiber in the two-fiber optical channel shared protection ring propagating the working second wavelength signal in a second direction opposite the first direction. The protection ring includes a monitor coupled to the two-fiber optical channel shared protection ring. The monitor is configured to detect at least one fault condition in the two-fiber optical channel shared protection ring. A plurality of switching nodes are interconnected by the two-fiber optical channel shared protection ring. Each switching node is responsive to the monitor. Each switching node includes an Nxc3x97N optical switch fabric system disposed in the node. The Nxc3x97N optical switch fabric includes 2N input/output (I/O) ports, wherein N is four, or an integer multiple of four. Each optical switch fabric is configured to switch at least one bi-directional channel. At least N three-port optical devices are coupled to N of the I/O ports. Each three-port optical device includes a bi-directional port coupled to an I/O port. The bi-directional port is configured to propagate the at least one bi-directional channel. At least one client add port is coupled to the input port, and at least one drop port is coupled to the output port.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.